Chip comprising an integrated circuit, fabrication method and method for locally rendering a carbonic layer conductive

ABSTRACT

A method can be used for locally rendering a carbonic isolating layer conductive. In one embodiment, a laser beam is directed onto the carbonic isolating layer so as to convert amorphous carbon of the carbonic isolating layer into graphite-like carbon. In another embodiment, the carbonic layer is heated so as to form a conducting portion of the layer so that a lateral path through the conducting portion connects two circuit elements of the integrated circuit.

TECHNICAL FIELD

This invention relates to a chip comprising an integrated circuit, to a fabrication method and to a method for locally rendering a carbonic layer conductive.

BACKGROUND

A chip usually comprises different layers formed on a substrate. The different layers may form a part of an integrated circuit such as interconnecting lines for circuit elements of the integrated circuit. In particular, the circuit elements are usually electrically connected to each other by conducting layers or conducting paths separated from each other by isolating layers. Such conducting paths are typically made of metal or polysilicon or other conducting materials. Methods for providing conducting paths, such as lift-off processes, result in embedding the paths in trenches of isolating layers. These methods comprise several processing steps for the embedding such as lithographic steps, structuring and chemical etching. One possibility is, for example, to fill trenches previously formed with conducting material, e.g., by a deposition process with a further step of chemical-mechanical polishing (CMP) in order to archive a planar surface of the isolation layer across the trenches after same have been filled with conducting material. Due to the several manufacturing steps the shown method for providing conducting paths is very labor intensive.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a chip comprising an integrated circuit and a carbonic layer, wherein the carbonic layer comprises a graphite-like carbon, and wherein a lateral conducting path through the graphite-like carbon electrically connects to circuit elements of the integrated circuit.

A further embodiment of the invention provides a chip comprising a substrate, an integrated circuit and a carbonic layer on the substrate, wherein the carbonic layer comprises an isolated portion comprising amorphous carbon and a conducting portion comprising graphite-like carbon, and wherein a lateral conducting path through the graphite-like carbon electrically connects two circuit elements of the integrated circuit.

Some embodiments of the invention provide a method for locally rendering a carbonic isolating layer conductive, wherein the method comprises the following steps: directing a laser beam onto the carbonic isolating layer so as to convert amorphous carbon of the carbonic isolating layer into graphite-like carbon.

Some embodiments of the invention provide a method for fabricating a chip comprising an integrated circuit and a carbonic layer, wherein the method comprises the following steps: heating the carbonic layer so as to form a conducting portion of the layer, wherein a lateral path through the conducting portion connects two circuit elements of the integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments according to the present invention will subsequently be discussed making reference to the enclosed figures in which:

FIG. 1 shows a cross sectional view through two layers of a chip and a top view of the chip comprising two circuit elements according an embodiment;

FIG. 2 shows a cross sectional view through three layers of a chip and a top view of the chip comprising two circuit elements according to an embodiment;

FIG. 3 shows a cross sectional view through four layers of a chip and a top view of the chip comprising two circuit elements according to an embodiment; and

FIG. 4 shows a cross sectional view through two layers of a chip and a top view of the chip comprising two circuit elements and a contact pad according to an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a chip 10 comprising an integrated circuit and a carbonic layer 12 formed on a further layer 14. The carbonic layer 12 may, for example, comprise CoSi or CoSi₂. The integrated circuit is substantially formed within layer 14, but for illustration purpose, merely two circuit elements 16 a and 16 b thereof are shown in FIG. 1. Layer 14 may, for example, comprise a semiconductor substrate or a semiconductor stack of a substrate and further layers between the substrate and layer 12. The two circuit elements 16 a and 16 b are formed in the further layer 14 at laterally distinct portions and may be, for example, a transistor, a capacitor and a diode, respectively. The circuit elements 16 a and 16 b are exemplarily shown as abutting an interface between layer 14 and layer 12. However, this is not necessary and alternatives will be shown hereinafter. Generally, the circuit elements 16 a and 16 b are connectable via lateral distinct portions of layer 12. At laterally surrounding portions, layer 14 has isolating material which electrically isolates the elements 16 a and 16 b, for example. The layer 12 has a thickness, e.g., 100 nm, and comprises a graphite-like carbon portion 18 which, in turn, may be surrounded by an isolating amorphous carbon portion of the layer 12. The isolating amorphous carbon portion of the layer 12 may, for example, comprise diamond-like carbon or be diamond-like carbon. The graphite-like carbon portion 18 in the layer 12 is illustratively shown to have the form of a line having a width w₁₈ which may, for example, be between 5 and 50 nm and a depth d₁₈ which may, for example, be between 3 and 300 nm. The graphite-like carbon portion 18 is arranged such that a lateral conducting path 18 through the graphite-like carbon electrically connects the two circuit elements 16 a and 16 b of the layer 14. In the embodiment of FIG. 1, the conducting path 18 continuously extends down to the surface of layer 12 interfacing to the lower layer 14 so that the conducting path 18 inherently interconnects all circuit elements 16 a and 16 b being connectable at portions of this surface overlapping the conducting path 18. However, alternative embodiments will be described below.

Thus, via the conducting path 18 an electrical current may be conducted, or control signals may be transmitted, from the circuit element 16 a to the circuit element 16 b of the integrated circuit, e.g., a logical circuit. The conducting path 18 through graphite-like carbon has an electrical conductivity, e.g., 0.5×10¹⁰ U/cm², which depends on the width w₁₈ and depth d₁₈ of the conducting graphite-like carbon portion 18. The conductivity may be chosen to be sufficient for transmitting control signals and low currents, for example.

In the following, a method for providing the lateral conducting path 18 is described. The layer 14 comprising the two circuit elements 16 a and 16 b is provided. The first step of the method is then to provide the carbonic isolating layer 12 onto the layer 14. The carbonic isolating layer 12 thus provided may, for example, comprise amorphous carbon and diamond-like carbon, respectively. Vapor depositing may be used. The next step is to locally heat the carbonic isolating layer 12 in a lateral area where the lateral conducting path 18 should be provided. A grid structure of the amorphous carbon and the diamond-like carbon, respectively, is destroyed by the local heating so as to covert the amorphous carbon to graphite-like carbon in said area. A grid structure of the graphite-like carbon enables electrical conductivity of same. Thus, the carbonic isolating layer 12 is (locally) rendered conductive in the areas so as to generate the conducting path 18 via the graphite-like carbon portion 18. The local heating may be performed by using a diffusively radiating heat source or by directing a laser beam onto the portion 18 of the carbonic isolating layer 12. Generally, an area where the conversion should take place, may be scanned by the heat source by moving a local heat spot over this area, such as a laser spot, or by covering surrounding areas besides the area of interest against the heating, e.g., by use of a mask and irradiating layer 12 at the non-masked portion.

Dependent on the duration of directing the laser beam onto the carbonic isolating layer onto a certain location and dependent on a power of the laser beam the depth d₁₈ of the graphite-like carbon 18 may be adjusted. In other words, due to absorbance, the heat intensively decreased from the side of layer 12 facing the heat source and the heating may be stopped at a location of layer 12 prior to the layer 12 completely converted along depth direction. This is, the depth d₁₈ of the conduction path 18 may be equal to the thickness of the layer 12, as shown in FIG. 1.

The thickness of the carbonic layer 12 and thus the depth d₁₈ of the portion 18 and the depth of the portion of amorphous carbon are constant. The described method does not change the topology of the layer 12 and thus main surfaces of the layer 12 are plane or approximately plane. The graphite-like carbon 18 may have the width w₁₈ which is smaller compared to the width of the connecting areas of the circuit elements 16 a and 16 b at the interface between the layer 12 and 14. The width w₁₈ of the graphite-like carbon portion 18 may be adjusted by varying the frequency of the laser or by varying a diameter of the laser beam. Alternatively, the width w₁₈ may be increased by providing two adjacent graphite-like carbon portions such that a broad graphite-like carbon portion is formed.

It is beneficial that the conducting path 18 may be provided by a simple and cost efficient method. A further advantage is that this method enables providing structured conductive paths embedded in the isolating layer 12 directly, without the need for a further step of planarization the surface of the layer 12, e.g., before providing further layers. Therefore, the mechanical stress for the chip 10 caused by filling trenches and by the planarization process is reduced.

In FIG. 2, a graphite-like carbon portion having a reduced depth when compared to the embodiment of FIG. 1 is discussed. FIG. 2 shows a further embodiment of a chip having three layers. A carbonic isolating layer 13 is arranged between the layer 14 and a layer 22. The first layer 14 at the first side of the layer 13 is equal to the layer 14 of the first embodiment. The second layer 22 at a second side of the layer 13 comprises two circuit elements 16 c and 16 d. The circuit elements 16 c and 16 d are formed on, or have connectable areas at, a surface of the upper layer 22 facing the layer 13. The layer 13 comprises amorphous carbon and graphite-like carbon which occupy laterally distinct areas of the carbonic layer 13. In this embodiment, the lateral conducting path 24 through the graphite-like carbon electrically connects the two circuit elements 16 c and 16 d. A first part 24 b of the graphite-like carbon portion 24 extends in a first lateral direction (in parallel with the layer stack) so as to extend between the position of the circuit element 16 c and a point 24 a. A second part 24 c extends in a second lateral direction through the layer 13, i.e., between the position of the circuit element 16 d and the point 24 a. That is, the conducting path 24 is shown in FIG. 2 illustratively to have a non-straight form. Differing from the embodiment of FIG. 1, the graphite-like carbon of the lateral conducting path 24 merely extends down to a depth d₂₄ which is smaller than the thickness of the carbonic layer 13 so that the circuit elements 16 c and 16 d are not electrically connected to each other by the conducting path 24. That is, the conducting path 24 is embedded in the isolating amorphous carbon of the layer 13 merely at one side of layer 13, and as the connecting areas of the circuit element 16 c and 16 d are located at opposite sides of the layer 13. Some are not electrically connected via the path 24, although path 24 overlaps both connecting areas. To be precise, circuit element 16 c is separated from the conducting path 24 via the isolating amorphous carbon portion along the thickness direction.

The graphite-like carbon of the conducting path 24 may be provided by local heating of the carbonic layer 13, for example, by directing a laser beam onto the carbonic isolating layer 13, as described above. In contrast to the embodiment of FIG. 1, the local heating of the carbonic layer 13 is performed by using a lower energy density of the laser compared to the embodiment of FIG. 1, for example. Alternatively, instead of reducing the power of the laser, the duration of directing the laser beam onto the layer 13 may be varied. The reduced power density of the laser or the shorter duration of directing the laser beam results in the reduced depth d₂₄ of the graphite-like carbon portion 24 when compared to the depth d₁₈ (see FIG. 1). In other words, the method enables forming the lateral conducting path 24 in the carbonic isolating layer 13 by using the laser, wherein the depth d₂₄ of the conducting path 24 is adjustable.

The layer 22 comprising the two circuit elements 16 c and 16 d may be provided before or after converting the amorphous carbon of the carbonic isolating layer into graphite-like carbon 24. In the latter case, in this embodiment, the step of directing the laser beam onto the carbonic isolating layer 13 may be performed so that the laser beam travels through the layer 22 before impinging onto the carbonic isolating layer 13 in the area of the portion 24. Here, parameters of the laser, e.g., frequency and power density, may be set such that the amorphous carbon of the layer 13 in the area of the portion 24 is converted into a graphite-like carbon while the characteristic of the layer 22 is not changed.

FIG. 3 illustrates a graphite-like carbon portion providing a lateral and vertical conducting path. FIG. 3 shows an embodiment of a chip having four layers. A layer 25 comprises the first circuit element 16 a while a layer 26 comprises the second circuit element 16 e. Between the layers 25 and 26 two isolating layers 28 and 30 are arranged. The isolating layer 28 comprises a via 32. The layer 30 is a carbonic layer comprising an amorphous carbon portion and a conductive graphite-like carbon portion 34. The lateral conducting path 34 electrically connects the circuit element 16 e arranged at a surface of the layer 26 facing layer 28 to the via 32 of the layer 28. The via 32 is electrically connected to the circuit element 16 a arranged at a surface of the layer 25 facing layer 30. Thus, the via 32 and the conducting path 34 laterally and vertically connect the two circuit elements 16 a and 16 e, i.e., through the two layers 28 and 30 and through the layer stack, respectively, and in parallel with the layers 25, 26, 28, 30.

The layer 30 may be provided and locally rendered conductive, as described above. The width w₃₄ of the graphite-like carbon portion 34 is shown exemplarily as being increased when compared to the width w₁₈ of the graphite-like carbon portion 18 according to the embodiment of FIG. 1. As a consequence of this, the electrical conductivity of the conduction path 34 is increased when compared to the conduction path 18 according to FIG. 1. The depth of the graphite-like carbon portion 34 extends over the whole thickness of the layer 30 in order to provide an electrical connection in a vertical direction from the via 32 in the lower layer 28 to the circuit element 16 e in the upper layer 26.

FIG. 4 illustrates a graphite-like carbon portion having a bifurcation and different depths at different locations of the graphite-like carbon portion. FIG. 4 shows a further embodiment having two layers 35 and 36. The layer 35 comprises two circuit elements 16 a and 16 f which are arranged at a surface of the layer 35 facing the layer 36. The carbonic layer 36 comprises a first portion of amorphous carbon and a second portion of graphite-like carbon 38 embedded in the amorphous carbon portion. The circuit element 16 a is electrically connected via a conducting path 38 in a first lateral direction through the graphite-like carbon 38 to a contact pad 38 a which is formed as a locally laterally enlarged portion of the graphite-like carbon. Via this contact pad 38 a, the chip may be electrically connected by a further via of a further (upper) layer arranged at a surface of layer 36. The enlarged shape of the contact pad 38 a enables, for example, accommodating positioning imprecision of the further layer or the further via, such as by lithographic processes used for defining the via. The contact pad 38 a has a geometry that is exemplarily square-shape and a part 38 c of the graphite-like carbon between the via 38 b and a position of the circuit element 16 a at an area 38 b extends down to a depth which is smaller than the thickness of the layer 36. The depth of the graphite-like carbon portion 38 extends over the whole thickness of the carbonic layer 36 in the area 38 b at the circuit element 16 a in order to electrically connect the circuit element 16 a via the surface of the layer 36.

The graphite-like carbon 38 comprises further a second part 38 d in a second lateral direction. A lateral conducting path through the second part 38 d of the graphite-like carbon electrically connects the circuit element 16 f to the circuit element 16 a and thus to the contact pad 38 a. Therefore, the graphite-like carbon 38 in an area 38 e at the circuit element 16 f extends over the whole thickness of the layer 36 while the depth of the part 38 d of the graphite-like carbon 38 is smaller than the thickness of the layer 36.

The carbonic layer 36 may be locally rendered conductive in the portion 38, as described with respect to the embodiment of FIG. 1. The depth differences between the areas 38 a, 38 c and 38 b as well as the depth differences between the areas 38 d and 38 e may, for example, be the result of using a different power density of the laser at different locations. The square shaped geometry of the contact pad 38 a or, in other words, the extensive surface of the contact pad 38 a may be generated by providing a plurality of adjacent graphite-like carbon portions.

According to another embodiment, instead of local heating laterally global heating may be performed so that a whole surface area of the carbonic isolating layer or an extensive area of the layer is converted into graphite-like carbon. This step may, for example, be performed by using an oven. Alternatively, the local heating may be performed by another heating source or by an ion source. It is beneficial that the extensive heating of the layer does not cause deformations of the layer or of a substrate.

Although some aspects have been described in the context of a method, these aspects also correspond to the chip 10 (see FIG. 1) comprising the carbonic layer 12 which comprises the conductive graphite-like carbon portion 18, wherein the lateral conducting path 18 through the graphite-like carbon 18 electrically connects to circuit elements 16 a and 16 b of the integrated circuit. As illustrated with respect to FIG. 1, the chip 10 may comprise an isolating portion which comprises amorphous carbon in which the graphite-like carbon 18 is embedded. The chip 10 may further comprise a substrate.

Although in some embodiments the circuit elements (e.g., 16 a, 16 b) and the conducting paths (e.g., 18) have been shown in a different layer (e.g., 12, 14), the invention also relates to embodiments in which at least one of the circuit elements and the graphite-like carbon of the conducting path are arranged in the same layer. 

What is claimed is:
 1. A method for locally rendering a carbonic isolating layer conductive, the method comprising: directing a laser beam onto the carbonic isolating layer so as to convert amorphous carbon of the carbonic isolating layer into graphite-like carbon.
 2. The method of claim 1, wherein directing the laser beam comprises forming a lateral conducting path within the graphite-like carbon portion such that an isolating portion that comprises amorphous carbon surrounds and abuts the graphite-like carbon.
 3. The method of claim 1, wherein directing the laser beam onto the carbonic isolating layer is performed so that the laser beam travels through a further layer before impinging onto the carbonic isolating layer. 